package Day2025_04_07;

import java.util.Arrays;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Demo03 {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int n = scan.nextInt();
        scan.nextLine();
        String s = scan.nextLine();
        char[] ss = s.toCharArray();
        Map<Character, Integer> hash = new HashMap<>();
        for (int i = 0; i < n; i++) {
            hash.put(ss[i], hash.getOrDefault(ss[i], 0) + 1);
        }
//        Arrays.sort((hash.) -> {
//
//        });
        int k = 0;
        for (char i = 'a'; i <= 'z'; i++) {
            if (hash.get(i) != 0) k++;
        }
    }

}
